Nonlinear Dynamics of Quantum-Dot Lasers: The Importance of Nonequilibrium Charge Carrier Dynamics

Benjamin Lingnau, Weng W. Chow, Eckehard Schöll, Kathy Lüdge

Technische Universitaet Berlin, Germany

In this work we explore the unique features of quantum-dot (QD) lasers in various dynamical applications. QD lasers have been the topic of ongoing research for more than a decade. Not only do they offer a variety of advantages in applications over conventional quantum-well (QW) lasers, but they also exhibit very interesting dynamics, e.g., under optical perturbations. These dynamics are strongly influenced by the charge carrier scattering between the bound QD states and off-resonant reservoir states in the device. A commomly used measure in describing the QD laser performance is the linewidth enhancement factor alpha, describing the coupling between gain and refractive index changes. We show that QD lasers can operate in strong nonequilibrium conditions which can lead to behavior that can no longer be characterized by alpha. Instead, a full nonequilibrium model must be used in order to understand the full dynamics. We present a microscopically based multi-rate-equation model used to simulate the QD laser dynamics. We apply this model to various setups and applications, including small and large signal modulation, optical feedback and injection, and highlight the differences when trying to use conventional rate equation models instead.